In addition to inventing the computer mouse, Doug Engelbart and his research team at SRI adapted a five key "keyset" for typing and entering commands with the left hand while pointing and clicking with the mouse.
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By pressing down the various keys on the keyset like keys on a piano – one at a time or in various combinations – you could type all the letters of the alphabet. In addition, they programmed the buttons on the mouse to work like shift keys and command keys when pressed while using the keyset. So for example, pressing the middle mouse button while typing on the keyset produced uppercase letters, while pressing the left-most mouse button produced numbers and punctuation instead of letters. Other mouse buttons served as command or ctrl key. Thus with mouse and keyset working together you could enter the equivalent of every key on the keyboard.
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Watch Doug introduce the keyset (1968)

Watch Doug using the keyset with mouse (1968)

The above footage is from the "Mother of All Demos" where Doug and his team first presented his visionary research. Visit Dougâs 1968 Demo on our website for more, including complete footage, photos, links, etc.
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The keyset was not intended to replace the keyboard, since it is much faster to type with both hands on a keyboard. But when one hand is using the mouse or otherwise occupied, it is much faster to type one-handed and enter shortcut keys using the keyset than the keyboard. The command user interface was designed to take advantage of this with easy to remember command shortcuts and a natural language verb noun command scheme. For example, the editing command to switch the places of two words is Transpose Word -- the user enters t for Transpose and w for Word with the keyset while moving the mouse to click once on each of the two words being switched, followed by a final click of the mouse for OK. In this environment, an experienced user could work with extraordinary speed and efficiency. Whereas the modern graphical user interface with menus and icons lowers the threshold for beginning users, Engelbart saw a need to offer a path for cultivating high-performance users. Watch Doug demo the keyset with mouse during his 1969 presentation, and watch others on his team using the keyset. Also watch Doug demo the user interface during his 1992 management seminar.

The keyset's five keys permit 31 combinations of pressed keys, enough to cover the alphabet and then some. Based on a simple progression from right to left, the keyset is actually simple to learn and use. The thumb presses "a", the index finger "b", the two pressing together produce "c", and so on.

Watch Doug's teaching method

Doug liked to teach children and adults by writing numbers on the finger pads of their left hand or on a traced image of their hand -- beginning with the thumb these are 1(thumb), 2(index), 4(middle), 8(ring), and 16(pinkie). Then he'd walk through counting with these numbered fingers -- your thumb is 1, your index finger is 2, Q: how do suppose you make 3? (A: your thumb and index finger together), your midddle finger is 4, Q: how do you make 5? (A: middle and thumb together), your middle and index fingers together make 6, Q: how do you make 7? (A: middle-index-thumb together), and so on. Now for letters of the alphabet. Letters progress the same way. For example, to get the 1st letter of the alphabet "a" you would press your thumb down on the keyset, to get the 2nd letter "b" press your index finger, Q: how do you make the 3rd letter "c"? (A: thumb and index), your middle finger is the 4th letter "d", and so forth. Often he would supply a cheat sheet listing numbers 1-26 in one column, and corresponding letters of the alphabet in the next column for easy reference. At this point in the lesson, Doug might have you try typing your name, and your friend's name. Then he might show you how to incorporate the mouse buttons to extend what you can type, such as pressing middle mouse button while typing letters to get uppercase, or left mouse button to get numbers and punctuation.

Knowing the simple progression speeds learning and makes it easier to remember. When you memorize the spelling of your name and you are well on your way. Kids learn this quickly, especially if you explain it is a silent "secret code" that they can use with their friends. If you love math you may have already cracked the code as a standard binary progression.

Tests performed in the early '60s showed that temporary secretarial helpers mastered the keyset in less than two hours no matter what method of training was used. They also demonstrated that the regular keyboard is more efficient for straightforward typing, but that for editing and maneuvering text, the mouse-keyset combination is the more efficient.

MouseSite - the definitive website on the Mouse hosted by Stanford University, especially their Photos of the First Mouse page. They also curate video of the 1968 demo and other significant archives from Doug Engelbart's work.

Screen-Selection Experiments: Display-Selection Techniques for Text Manipulation, William K. English, Douglas C. Engelbart and Melvyn L. Berman, March 1967. This paper describes an experimental study into the relative merits of different CRT display-selection devices as used within a real-time, computer-display, text-manipulation system in use at Stanford Research Institute. The mouse was tested against other devices and found to be the most accurate and efficient. See also the 1965 Report and the 1966 Quarterly Report detailing screen-selection experiments.

"The Mother of All Demos" (90 min Video/Film) Doug's 1968 debut of NLS (Augment's precursor) including hypermedia, the mouse, collaborative work, interactive computing, human computer interface, and overarching guiding principles. See especially Clip 12 where Doug, sitting in San Francisco, brings in a coworker sitting in his lab in Menlo Park, to demonstrate the mouse, and Clip 13 where Doug introduces the keyset.